1. Field of the Invention
The present invention relates to a color correction system having a converter which can correct image colors handled by an imaging apparatus and a color reproduction system which can realize faithful color reproduction and ensure high reliability of transfer color data among light source colors such as displayed colors and non-luminous object colors such as reflected colors and transmitted colors.
2. Description of the Prior Art
As order receiving systems for various kinds of products have been computerized recently, opportunities of deciding colors of products by using image data on a monitor display screen have been increased. Therefore, development of an imaging apparatus and system which can faithfully transmit and reproduce displayed colors on the monitor display screen is expected.
As a method for faithfully reproducing displayed colors on the monitor display screen, a method for converting input signals equivalent to the light source colors displayed on the monitor display screen to color parameters (tristimulus values determined by CIE (Commission Internationale de l'Eclairage)) of the non-luminous object colors which are the colors of a product is known. For example, the mutual conversion method disclosed in Japanese Patent Application Laid-Open No. 2-22523 will be explained with reference to FIG. 2. In FIG. 2, a color comparison environment in which an observer 213 can observe a color matching area 209 in an achromatic color background 208 on the display screen of a CRT display 207 and a standard color chip 212 in an achromatic color object background 211 which is lighted by an illuminator 210 at the same time is provided. A light shielding board 214 is installed so as to prevent the CRT display 207 from irradiation of the illuminating light of the illuminator 210. Input signals into the CRT display 207 can be adjusted so that the color of the color matching area 209 matches the color of the standard color chip 212 in visual observation by the observer 213. In this color comparison environment, the mutual conversion method between the CIE tristimulus values of the standard color chip 212 which are known and the above input signals into the CRT display 207 is proposed by the chromaticity of luminescent material on the CRT display 207 and linear operation of the function expression of the gamma-th power characteristics. Furthermore, other inventions of the applicant which are related to the present invention are disclosed in Japanese Patent Application Laid-Open Nos. 5-69574 and 6-17998 (U.S. patent application Ser. No. 08/219,271, now U.S. Pat. No. 5,526,058).
For the art of color correction, design creation using a computer graphic apparatus is executed in various industrial fields such as cloth and accessory, apparel, automobile, domestic electric appliances, printing, and others. In these uses, not only rough color designing but also final designing or up to decision of design colors in a stage close to it are being increasingly often executed on a computer graphic apparatus.
Therefore, an art for eliminating a difference between a color on the color display screen of a computer graphic apparatus or on a printing paper of a color printer which is decided by visual evaluation of a designer and a color displayed on an actual trial product or on a product obtained by manufacture so as to produce the same color and for facilitating decision of a color by visual evaluation of a designer is necessary (when there is a difference between them such that they are not the same color, it is necessary to decide a color by visual evaluation in anticipation of the difference, so that the operation of visual evaluation will be much more complicated).
As one of the aforementioned arts, a system which can precisely control and define a color of a color display is disclosed in Japanese Patent Application Laid-Open No. 1-147989 (Japanese Patent Publication No. 4-44277) which corresponds to U.S. Pat. No. 4,843,573. This prior art will be explained hereunder with reference to FIG. 10. FIG. 10 is a block diagram showing the schematic constitution of a computer graphic apparatus. In the drawing, the computer graphic apparatus is constructed by connecting a color display 801 using a color CRT (cathode ray tube) 802 to a graphics workstation 805 including an input device 810 such as a keyboard, a programmable processor 808, and a memory 809 as shown in the drawing.
A user realizes and calculates a color space using the graphics workstation 805 and can designate the display color on the color CRT 802 by inputting color space coordinates from the input device 810. The color space used by this prior art is a uniform color space on the basis of the international standard system of the Commission Internationale de l'Eclairage (CIE) and indicates a perceptively uniform color change for a change in the color coordinates. When the display color to be displayed on the color CRT 802 is inputted from the input device 810, by predicting a color change (mismatch) between the displayed color on the color CRT 802 and the actual color which is calculated and realized by the graphics workstation 805 to a certain extent, the user can select the color efficiently on the input device 810.
In the aforementioned conventional example relating to a color reproduction system, although the color comparison environment is provided, a judgment of color matching is executed on the basis of visual comparison between colors. Therefore, there is a worry about variations in color matching accuracy between the light source color on the monitor display screen and the non-luminous object color due to the effect of the dependency of an observer for judgment of color matching. The dependency on the color comparison environment and imaging apparatus cannot be ignored and a problem of deterioration of color reproduction relating to color matching due to variations per hour of the imaging apparatus or variations in products arises. Particularly when transfer color data or retention color data is reproduced, there is a worry about remarkable reduction of the reliability of reproduced colors.
Color selection on the input device 810 according to the aforementioned prior art relating to a color correction system is based on the color coordinates or each primary color luminance data stored in the memory 809 and gradation correction, white balance adjustment, and variations in the luminescent material of the color CRT 802 are anticipated in the data. However, although the data may be calibrated periodically after it is set before the computer graphic apparatus is delivered from the factory, it is little compensated for the setting status of the color display 801 by the user and changes in the use environment.
Therefore, when a plurality of colors coexist as displayed colors like in a case wherein a natural picture is displayed on the color display 801, it is very difficult to reproduce each color faithfully. Furthermore, on the assumption that the reproduced color for the same color data is different between different kinds of imaging apparatuses which handle color images, it is necessary that a user makes a color design by keeping the corresponding color corresponding to the color data in mind.